CSS-Positionierung – Absolut, Relativ, Fest und Sticky.

Lecture 11: CSS Positioning – Absolute, Relative, Fixed, and Sticky

Welcome to the eleventh lecture of the "Basic to Brilliance" course. In this lecture, we will explore the different types of CSS positioning: relative, absolute, fixed, and sticky. Understanding positioning allows you to control where elements appear on a page and how they behave as users interact with the content.

1. Understanding the position Property

The position property specifies how an element is positioned in the document. It can take the following values:

• static: Default value. Elements are positioned according to the normal document flow.
• relative: Element is positioned relative to its normal position.
• absolute: Element is positioned relative to its nearest positioned ancestor or the initial containing block.
• fixed: Element is positioned relative to the browser window and remains in the same position when scrolling.
• sticky: Element is treated as relative until it reaches a threshold (e.g., a scroll position), and then it becomes fixed.

2. Relative Positioning

An element with position: relative is positioned relative to its original (static) position. It remains in the document flow, meaning other elements will still take it into account.

• Example: Using relative positioning to move an element.

  .box {
    position: relative;
    top: 20px; /* Moves the box 20px down from its normal position */
    left: 30px; /* Moves the box 30px to the right */
  }

In this example, the element is shifted down by 20px and to the right by 30px from its original position, but its space in the document flow is preserved.

3. Absolute Positioning

Elements with position: absolute are removed from the document flow and positioned relative to their nearest positioned ancestor (i.e., an ancestor with a position other than static).

• Example: Absolutely positioning an element inside a container.

  .container {
    position: relative; /* This container is the reference for the absolute positioning */
    width: 300px;
    height: 200px;
    background-color: #f4f4f4;
  }

  .box {
    position: absolute;
    top: 50px;
    right: 20px;
    background-color: #333;
    color: white;
    padding: 10px;
  }

In this example:

• The .box is absolutely positioned 50px from the top and 20px from the right inside the .container element.
• The .container has position: relative, making it the positioning reference for the .box.

4. Fixed Positioning

An element with position: fixed is positioned relative to the browser window, regardless of how the page is scrolled.

• Example: Creating a fixed navigation bar.

  .navbar {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    background-color: #333;
    color: white;
    padding: 15px;
    text-align: center;
  }

In this example:

• The .navbar is positioned at the top of the viewport and remains fixed even when the page is scrolled.

5. Sticky Positioning

An element with position: sticky is treated as relative until the user scrolls past a defined threshold, at which point it becomes fixed.

• Example: Sticky header that stays at the top after scrolling.

  .header {
    position: sticky;
    top: 0;
    background-color: #333;
    color: white;
    padding: 10px;
  }

In this example:

• The .header behaves like a normal element until it reaches the top of the page. After that, it sticks to the top and remains visible as the user scrolls.

6. Z-Index

When elements are positioned (either relative, absolute, fixed, or sticky), you can control their stacking order using the z-index property. Higher z-index values make elements appear above lower ones.

• Example: Controlling the stacking order.

  .box1 {
    position: absolute;
    top: 50px;
    left: 50px;
    z-index: 1; /* Lower z-index */
    background-color: #f4f4f4;
    padding: 20px;
  }

  .box2 {
    position: absolute;
    top: 80px;
    left: 80px;
    z-index: 2; /* Higher z-index */
    background-color: #333;
    color: white;
    padding: 20px;
  }

In this example:

• .box2 will appear above .box1 due to its higher z-index value.

7. Combining Positioning Techniques

You can combine positioning values to create advanced layouts.

• Example: Fixed sidebar with relative content area.

  .sidebar {
    position: fixed;
    top: 0;
    left: 0;
    width: 200px;
    height: 100vh;
    background-color: #333;
    color: white;
    padding: 20px;
  }

  .content {
    position: relative;
    margin-left: 220px; /* Account for the fixed sidebar */
    padding: 20px;
  }

In this layout:

• Le .sidebar est fixé à gauche de la page et reste visible lors du défilement.
• La zone .content est positionnée de manière relative et ajuste sa marge pour tenir compte de la barre latérale.

Exercice pratique

1. Créez une page Web avec un en-tête et un pied de page fixes, et utilisez un positionnement relatif et absolu pour le contenu.
2. Ajoutez une barre latérale collante qui se fixe lors du défilement.

Prochaine étape : Dans la prochaine conférence, nous plongerons dans les Transformations et animations CSS, où vous apprendrez à animer facilement vos éléments Web. Préparez-vous à rendre vos créations dynamiques et interactives !

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Ridoy Hasan

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